The present invention relates to an improvement in the method of positioning a beam to a specific portion of a semiconductor wafer, which is required in a semiconductor manufacturing process.
In semiconductor manufacturing processes, such as an electron beam exposure and an ion implantation, it is frequently required to position a specific area with high accuracy, for example, an area to be processed, at a predetermined location on the semiconductor wafer in the semiconductor manufacturing apparatus. The recent trend in this field is to increase micro-miniaturization and a high integration density of semiconductor integrated circuits. With this trend, the requirement for the positioning accuracy is more strict.
A lithography apparatus is used for effecting the electron beam exposure or the optical exposure. In this apparatus, it is necessary to position the semiconductor wafer at a predetermined position required in an optical system of the apparatus. For the positioning, the positions of positioning marks, previously formed on the semiconductor wafer, are measured. The measurement results are used for obtaining a parallel movement component and a rotating movement component of the required movement of the whole semiconductor wafer.
To improve the positioning accuracy of the semiconductor wafer, positioning marks are arrayed in a matrix fashion, for example. The positioning is made for each mark or for each chip area to be formed on the wafer. This approach can correct a dislocation of the wafer due to the distortion of the wafer caused during the manufacturing process. Types of defects of the positioning marks are classified into:
(a) The mark is not present. PA1 (b) The mark is dislocated from its correct position. PA1 (c) Dust is stuck to the mark or the mark is deformed with projected or chipped portions, so that the mark cannot be accurately measured.
Use of such defective marks brings about impossible positioning or inaccurate positioning of the semiconductor wafer. For example, the defective mark of the type (a) makes it impossible to position the semiconductor wafer. The defective mark of the type (b) or (c) makes the positioning inaccurate. Thus, the conventional positioning method can not provide an accurate positioning of the wafer when the defective mark is contained in the positioning marks. For example, the conventional positioning method makes it difficult to provide a fine pattern on any semiconductor chip with high precision. In this respect, the conventional positioning method involves the problem to be solved before attaining semiconductor devices improved in accuracy, integration density, production yield, and uniformity in the characteristics over the wafer surface.